The site of Orgnac 3 (Central France) is known for its 11 metres thick stratigraphic sequence that encompasses the appearance of Levallois debitage. Originally a cave, the site gradually became a rock shelter and eventually an open-air site. 50,000 stone tools were found, alongside abundant faunal remains and a series of Homo heidelbergensis teeth (from the middle levels). Biostratigraphy places the lower levels (8-3) in MIS-9 and the upper levels (1-2) in MIS-8. A new study in PloS ONE reports on the application of a new series of U/Th and 40Ar/39Ar methods to refine the dating of the site and come to a better understanding of the emergence of the Middle Palaeolithic (as defined by the onset of Levallois reduction).
At Orgnac gradual changes over time towards Middle Palaeolithic-type behaviour can be observed. The lower levels are characterised by a broad diversity of flake tools alongside centripetal cores. Levallois debitage starts to appear in the middle levels (4b-4a) and becomes dominant at the top of the sequence (3-1), which coincides with a very low number of handaxes and a dominance of scrapers. Previous attempts to date the site (U/Th and ESR) resulted in dates with very large error margins (e.g. +76−42 ka). Therefore, the team obtained a new set of dates, including fourteen U/Th dates on speleotherms from lower levels 5b, 6 and 7, and 57 40Ar/39Ar dates on sanidine grains from upper level 2.
Results for the first time date a Middle Pleistocene site with a relatively good precision, with the 40Ar/39Ar dating giving a weighted mean age of 302.9 ± 2.9 ka (2σ). The U/Th method gave an age range of 265-312 ka. While generally consistent, there are some issues with matching up the results of the two techniques and therefore the team are planning on carrying out 40Ar/39Ar dating on single grains in the near future.
However, these dates do indicate a minimum age of 265 ka for level 5b, which testifies to the first appearance of Levallois flaking at the site, making Orgnac 3 one of the oldest sites with systematic use of Levallois reduction, supporting the claim that the Middle Palaeolithic emerged in Europe about 300,000 years ago (MIS 9/8).
Reference: Michel V, Shen G, Shen C-C, Wu C-C, Vérati C, et al. (2013) Application of U/Th and 40Ar/39Ar Dating to Orgnac 3, a Late Acheulean and Early Middle Palaeolithic Site in Ardèche, France. PLoS ONE 8(12): e82394.